1. Field of the Invention
This invention relates to systems and methods for transmission of still images over relatively low-speed communication channels. More specifically the invention relates to progressive image streaming over low speed communication lines, and may be applied to a variety of fields and disciplines, including commercial printing, medical imaging, among others.
2. Brief Description of the Prior Art
In a narrow bandwidth environment, a simple transfer to a client computer of any original image stored in a server's storage is obviously time consuming. In many cases the user only wishes to view a low resolution of the image and perhaps a few more high resolution details, and so a full image transfer is inefficient. This problem can be overcome by storing images in some compressed formats. Examples for such formats are standards such as Progressive JPEG, FlashPix, the upcoming JPEG2000, and some recent proprietary so-called wavelet formats. Some of these formats allow progressive transmission (of the full image) and some allow transmission of only region of interest (ROI) data, thereby avoiding the necessity to transmit the entire image before it can be rendered at the client side.
But there are at least three main problems with the existing solutions: first, one needs to prepare and store a compressed image of this type for any original image located in the storage. In many cases this results in storing both the original image and the compressed version. Sometimes the size of the file prepared for transmission is even larger than the original file. For example, a lossless FlashPix representation of a given image is typically 4/3 the size of the original image. Secondly, the computation of any of the above formats is much more intensive than regular compression techniques such as the base-line version of JPEG. The last problem is that the existing methods generally do not support efficient extraction and transmission of ROI data, but rather the whole image in progressive mode. The FlashPix format that does support ROI streaming is not a wavelet-based format and therefore cannot take advantage (as wavelets do) of the relations between the various resolutions of the image.
The above-mentioned problems with the prior art result in inefficient systems both in architecture and data handling workflows. This tends to be the case for imaging applications such as in the graphics arts and medical environments, where image files are relatively large and they are created dynamically as external events dictate.